The invention relates to a catalyzer for burning at least part of a fuel/oxidant mixture flowing through the catalyzer.
U.S. Pat. No. 5,346,389, U.S. Pat. No. 5,202,303, U.S. Pat. No. 5,437,099, and U.S. Pat. No. 5,328,359 disclose catalyzers of an initial type, each of which comprises several catalytically active channels and several catalytically inactive channels. The known catalyzers are produced using zigzag-shaped corrugated or folded sheets that are layered by way of a helical winding or by folding back and forth. The corrugations or folds then form the channels of the catalyzer. One side of the respective sheet is constructed catalytically active by way of a catalyzer coating. In this way, the layering or stacking creates the catalytically active channels and the catalytically inactive channels. The conversion or combustion of the fuel/oxidant mixture takes place inside the coated or catalytically active channels. In essence, no conversion or combustion of the mixture takes place in the uncoated or catalytically inactive channels, so that this part of the mixture flow can be used for removing heat, i.e. for the cooling of the catalyzer.
Because of the one-sided coating with catalyzer material and a corresponding stacking or layering of the sheets used to construct the catalyzer, a catalyzer construction can be achieved, in which approximately half of all channels are completely catalytically coated, while the other half of the channels are uncoated. In this embodiment, the temperature increase in the catalyzer can be effectively reduced since the combustion of the mixture in the catalyzer is limited to the catalytically active channels and therefore to approximately 50%. This construction makes it possible to prevent an overheating of the catalyzer that could result in its destruction.
U.S. Pat. No. 4,154,568 discloses a catalyzer of a principally different construction with several monolith blocks arranged consecutively in the main flow direction. The monolith blocks contain channels that are all catalytically active and extend parallel to the main flow direction. The channels of a monolith block located downstream have a smaller flow cross-section than those of the monolith block located upstream. This is meant to achieve a complete combustion of the fuel/oxidant mixture inside the catalyst, while in the catalyzers of this class, only part of the gas mixture is supposed to be burned.
In the catalyzers of the initially mentioned type, the catalytically active channels and the catalytically inactive channels result in a reduction of the fuel conversion, and thus in a reduction of the operating temperature of the catalyzer, so that sufficiently long lives can be achieved for said catalyzer. In a construction with 50% catalytically active channels and 50% catalytically inactive channels, the maximum achievable degree of conversion of the fuel is reduced to 50%. This also has the result that the fuel concentration at the catalyzer outlet over the cross-section is subject to high fluctuations. While almost no fuel exits from the catalytically active channels then, the almost unchanged fuel/oxidant mixture flows from the catalytically inactive channels. If an ignition of the mixture occurs before it mixes downstream from the catalyzer, the subsequent combustion reaction may result in temperature peaks in the catalyzer that are associated with the production of harmful substances, in particular NOX.
Another problem is that the conversion of the fuel inside the catalytically active channels only achieves the desired degree of conversion if a sufficiently long channel length exists. This is attributed to the fact that, on the one hand, the fuel content decreases in flow direction, and, on the other hand, the thickness of the boundary layer increases. In order to achieve a high degree of conversion, a conventional catalyzer therefore is relatively long in the main flow direction, which is associated with relatively high-pressure losses.
The invention means to remedy this. The invention is concerned with disclosing an improved embodiment, in particular with a compact construction, for a catalyzer of the initially mentioned type.
In an exemplary embodiment, a catalyzer for burning at least part of a fuel/oxidant mixture flowing through the catalyzer has several catalytically active channels and several catalytically inactive channels. In a longitudinal section of the catalyzer spaced apart from the inflow side of the catalyzer in the main flow direction, one or more from the group of turbulators are arranged in at least several catalytically active channels and connections are formed at least between several catalytically active channels and catalytically inactive channels enabling a flow between catalytically active channels and catalytically inactive channels.
In an exemplary embodiment, a catalyzer for burning at least a part of a fuel/oxidant mixture flowing through the catalyzer has a plurality of catalytically active channels and a plurality of catalytically inactive channels, and one or more from the group of a plurality of turbulators and a plurality of connections. Each channel has a first longitudinal portion upstream in a main flow direction of a second longitudinal portion. The plurality of turbulators are arranged in the second longitudinal portion of at least several of the catalytically active channels and the plurality of connections are formed in the second longitudinal portion between at least several catalytically active channels and catalytically inactive channels to operatively exchange a gas between the catalytically active channels and the catalytically inactive channels.